When a card enters the realm as a copy, e.g. Mirror Realm or Selfsame Simulacrum, its characteristics and abilities match the copied card. If the copying card (e.g. Selfsame Simulacrum) leaves the realm, it reverts to its printed characteristics and abilities. When you create a copy, e.g. an artifact via Replication or a magic via Archimago or Orb of Ba'al Berith, the characteristics and abilities match those printed on the copied card, and the copy is a token. For example, in the case of a copied magic, it will be banished as soon as it resolves from the storyline, per the normal token rules.